Binary toxin and its clinical importance in Clostridium difficile infection, Belgium

The Strain and the Clinical Outcome of Clostridioides difficile Infection: A Meta-analysis

Background

The association between bacterial strains and clinical outcomes in Clostridioides difficile infection (CDI) has yielded conflicting results across studies. We conducted a systematic review and meta-analyses to assess the impact of these strains.

Methods

Five electronic databases were used to identify studies reporting CDI severity, complications, recurrence, or mortality according to strain type from inception to June 2022. Random effect meta-analyses were conducted to assess outcome proportions and risk ratios (RRs).

Results

A total of 93 studies were included: 44 reported recurrences, 50 reported severity or complications, and 55 reported deaths. Pooled proportions of complications were statistically comparable between NAP1/BI/R027 and R001, R078, and R106. Pooled attributable mortality was 4.8% with a gradation in patients infected with R014/20 (1.7%), R001 (3.8%), R078 (5.3%), and R027 (10.2%). Higher 30-day all-cause mortality was observed in patients infected with R001, R002, R027, and R106 (range, 20%-25%).NAP1/BI/R027 was associated with several unfavorable outcomes: recurrence 30 days after the end of treatment (pooled RR, 1.98; 95% CI, 1.02-3.84); admission to intensive care, colectomy, or CDI-associated death (1.88; 1.09-3.25); and 30-day attributable mortality (1.96; 1.23-3.13). The association between harboring the binary toxin gene and 30-day all-cause mortality did not reach significance (RR, 1.6 [0.9-2.9]; 7 studies).

Conclusions

Numerous studies were excluded due to discrepancies in the definition of the outcomes and the lack of reporting of important covariates. NAP1/BI/R027, the most frequently reported and assessed strain, was associated with unfavorable outcomes. However, there were not sufficient data to reach significant conclusions on other strains.

An Update on Clostridioides difficile Binary Toxin

Infection with Clostridioides difficile (CDI), a common healthcare-associated infection, includes symptoms ranging from mild diarrhea to severe cases of pseudomembranous colitis. Toxin A (TcdA) and toxin B (TcdB) cause cytotoxicity and cellular detachment from intestinal epithelium and are responsible for CDI symptomatology. Approximately 20% of C. difficile strains produce a binary toxin (CDT) encoded by the tcdA and tcdB genes, which is thought to enhance TcdA and TcdB toxicity; however, the role of CDT in CDI remains controversial. Here, we focused on describing the main features of CDT and its impact on the host, clinical relevance, epidemiology, and potential therapeutic approaches.

Defining the black box: a narrative review of factors associated with adverse outcomes from severe Clostridioides difficile infection

In the United States, Clostridioides difficile infection (CDI) is the leading cause of healthcare-associated infection, affecting nearly half a million people and resulting in more than 20,000 in-hospital deaths every year. It is therefore imperative to better characterize the intricate interplay between C. difficile microbial factors, host immunologic signatures, and clinical features that are associated with adverse outcomes of severe CDI. In this narrative review, we discuss the implications of C. difficile genetics and virulence factors in the molecular epidemiology of CDI, and the utility of early biomarkers in predicting the clinical trajectory of patients at risk of developing severe CDI. Furthermore, we identify associations between host immune factors and CDI outcomes in both animal models and human studies. Next, we highlight clinical factors including renal dysfunction, aging, blood biomarkers, level of care, and chronic illnesses that can affect severe CDI diagnosis and outcome. Finally, we present our perspectives on two specific treatments pertinent to patient outcomes: metronidazole administration and surgery. Together, this review explores the various venues of CDI research and highlights the importance of integrating microbial, host, and clinical data to help clinicians make optimal treatment decisions based on accurate prediction of disease progression.

Randomized Controlled Trial of Oral Vancomycin Treatment in Clostridioides difficile-Colonized Patients

A gold standard diagnostic for Clostridioides difficile infection (CDI) does not exist. An area of controversy is how to manage patients whose stool tests positive by nucleic acid amplification tests but negative by toxin enzyme immunoassay.

Clostridioides difficile infection (CDI) is most commonly diagnosed using nucleic acid amplification tests (NAAT); the low positive predictive value of these assays results in patients colonized with C. difficile unnecessarily receiving CDI treatment antibiotics. The risks and benefits of antibiotic treatment in individuals with such cases are unknown. Fecal samples of NAAT-positive, toxin enzyme immunoassay (EIA)-negative patients were collected before, during, and after randomization to vancomycin (n = 8) or placebo (n = 7). C. difficile and antibiotic-resistant organisms (AROs) were selectively cultured from fecal and environmental samples. Shotgun metagenomics and comparative isolate genomics were used to understand the impact of oral vancomycin on the microbiome and environmental contamination. Overall, 80% of placebo patients and 71% of vancomycin patients were colonized with C. difficile posttreatment. One person randomized to placebo subsequently received treatment for CDI. In the vancomycin-treated group, beta-diversity (P = 0.0059) and macrolide-lincosamide-streptogramin (MLS) resistance genes (P = 0.037) increased after treatment; C. difficile and vancomycin-resistant enterococci (VRE) environmental contamination was found in 53% of patients and 26% of patients, respectively. We found that vancomycin alters the gut microbiota, does not permanently clear C. difficile, and is associated with VRE colonization/environmental contamination. (This study has been registered at ClinicalTrials.gov under registration no. NCT03388268.)

IMPORTANCE A gold standard diagnostic for Clostridioides difficile infection (CDI) does not exist. An area of controversy is how to manage patients whose stool tests positive by nucleic acid amplification tests but negative by toxin enzyme immunoassay. Existing data suggest most of these patients do not have CDI, but most are treated with oral vancomycin. Potential benefits to treatment include a decreased risk for adverse outcomes if the patient does have CDI and the potential to decrease C. difficile shedding/transmission. However, oral vancomycin perturbs the intestinal microbiota and promotes antibiotic-resistant organism colonization/transmission. We conducted a double-blinded randomized controlled trial to assess the risk-benefit of oral vancomycin treatment in this population. Oral vancomycin did not result in long-term clearance of C. difficile, perturbed the microbiota, and was associated with colonization/shedding of vancomycin-resistant enterococci. This work underscores the need to better understand this population of patients in the context of C. difficile/ARO-related outcomes and transmission.

Structure of the cell-binding component of the Clostridium difficile binary toxin reveals a di-heptamer macromolecular assembly

Targeting Clostridium difficile infection is challenging because treatment options are limited, and high recurrence rates are common. One reason for this is that hypervirulent C. difficile strains often have a binary toxin termed the C. difficile toxin, in addition to the enterotoxins TsdA and TsdB. The C. difficile toxin has an enzymatic component, termed CDTa, and a pore-forming or delivery subunit termed CDTb. CDTb was characterized here using a combination of single-particle cryoelectron microscopy, X-ray crystallography, NMR, and other biophysical methods. In the absence of CDTa, 2 di-heptamer structures for activated CDTb (1.0 MDa) were solved at atomic resolution, including a symmetric (SymCDTb; 3.14 Å) and an asymmetric form (AsymCDTb; 2.84 Å). Roles played by 2 receptor-binding domains of activated CDTb were of particular interest since the receptor-binding domain 1 lacks sequence homology to any other known toxin, and the receptor-binding domain 2 is completely absent in other well-studied heptameric toxins (i.e., anthrax). For AsymCDTb, a Ca2+ binding site was discovered in the first receptor-binding domain that is important for its stability, and the second receptor-binding domain was found to be critical for host cell toxicity and the di-heptamer fold for both forms of activated CDTb. Together, these studies represent a starting point for developing structure-based drug-design strategies to target the most severe strains of C. difficile.

Association between Clostridioides difficile ribotypes, restriction endonuclease analysis types, and toxin gene expression

OBJECTIVES

Clostridioides difficile strains cause severe infection. Previous studies suggested that the virulence of C. difficile is dependent on ribotype; however, this hypothesis is still controversial. We aim to investigate the relationship between ribotypes, restriction endonuclease analysis (REA) types, and toxin gene expression in C. difficile strains.

METHODS

We utilized 53 clinical C. difficile strains. All strains were assigned a molecular strain type using PCR ribotyping and REA typing and classified into 17 ribotypes and six REA types. The expression of toxin genes (tcdA, tcdB, and cdtB) in C. difficile strains were quantified by real-time PCR using each specific primer set, and expression was normalized to that of the housekeeping gene rpoA.

RESULTS

All 53 strains expressed tcdB and four strains expressed cdtB. Five strains did not express tcdA. Most ribotype and REA type strains expressed tcdA and tcdB similar to the BAA-1870 strain. In cdtB-positive strains, the cdtB expression levels were similar to those in the BAA-1870 strain. tcdA and tcdB expression levels were similar in the cdtB-positive and cdtB-negative strains.

CONCLUSION

Toxin gene expression was not associated with the ribotype. Production of binary toxin C. difficile transferase was not related to tcdA and tcdB expression levels.

Fidaxomicin for treatment of Clostridium difficile infection in clinical practice: a prospective cohort study in a French University Hospital

PURPOSE

Two randomized controlled trials (RCTs) showed the non-inferiority of fidaxomicin compared with vancomycin for Clostridium difficile infection (CDI) treatment and its superiority regarding recurrence rate. The aim of this study was to evaluate fidaxomicin's efficacy in clinical practice.

METHODS

This single-center prospective cohort study included hospitalized patients treated with fidaxomicin for CDI. Demographic, clinical and biological data were collected. Primary outcome was efficacy of fidaxomicin (clinical cure, recurrence and global cure) at 10 weeks. Secondary outcome was efficacy among different subgroups.

RESULTS

Ninety-nine patients were included: 42 severe CDI, 16 complicated CDI and 41 recurrent CDI. Rates of clinical cure, recurrence and global cure were 87, 15 and 59%, respectively. Subgroup analysis showed a higher recurrence rate for patients with recurrent CDI compared with first episode (8 vs. 26%; p = 0.04). Binary toxin was associated with severe/complicated CDI (80 vs. 50%; p < 0.01) and recurrence (32 vs. 7%; p < 0.01). Fidaxomicin was used as a first line for 83% of the patients with recurrence and for only 52% of first episodes even though 86% had recurrence's risk factors.

CONCLUSION

Compared with RCTs, fidaxomicin in real world is used for patients with more severe and recurrent CDI, but clinical cure and recurrence rates were similar. Comparative studies are needed in these specific subgroups. Our data also illustrate clinicians' difficulty to define a "patient at risk for recurrence" among the first episodes. Finally, we showed that binary toxin could be important in the screening for severity and recurrence risks.